You have to set your gains correct, with a DIMM, O-scope, or a DD 1. Clipping can come from your headunit, not from wiring down to 1 OHm.
I guess you to wire down to 1 Ohm and go with 2 of those boy´s http://www.ebay.com/itm/AUDIOPIPE-AP15001D-1500W-MONO-D-Audio-Amplifier-/390397265695?pt=Car_Amplifiers&hash=item5ae57d871f, there is a ampclamptestcomparsion of 1500 watt amps from Fecupe and this bugger put
a little bit over 1800 RMS watt´s @ 14.x volt´s out. From the rest of the money you can buy a DD 1 to set your gains correct.